Recirculation of exhaust gases has been employed in automotive engines to inhibit the formation and emission of oxides of nitrogen. In general, it is desired to vary the proportion of exhaust gases which are recirculated in accordance with changes in engine operating conditions; for example, in a diesel engine it is desired to increase recirculation as the throttle reduces fuel flow, to increase recirculation with engine speed, and to reduce recirculation with a decrease in the ambient atmospheric pressure. The exhaust gas recirculation valve is frequently operated by a diaphragm responsive to a subatmospheric control pressure, and various electrical, pneumatic and mechanical devices have been employed to establish the desired control pressure.